FULL WAFER OPTICAL CHARACTERIZATION NF RESONANT-TUNNELING STRUCTURES USING PHOTOLUMINESCENCE EXCITATION SPECTROSCOPY

We report on a novel optical technique for accurately characterising u nprocessed GaAs/AlGaAs tunnelling structures having two or more thin b arriers and thick, heavily doped, contact layers. The results from pho toluminescence excitation spectroscopy measurements are presented in w hich the intensity of the photoluminescence from the heavily doped con tact layers rather than photoluminescence from the quantum wells is mo nitored. This method gives essential information for growth and qualit y control of ''as-grown'' layers prior to device fabrication. The usef ulness and precision of this technique is illustrated by the measureme nt of a 0.3% variation in layer thickness from the centre to the edge of an as-grown wafer, and a 1% wafer to wafer variation in layer thick ness in a series of triple barrier resonant tunnelling structures that have been designed for use at THz frequencies.